In my copending application Ser. No. 07/602,504 filed Oct. 24, 1990, U.S. Pat. No. 5,150,195 there is disclosed an adhesive formulation, suitable for bonding semiconductor devices to a substrate, which can be rapidly cured. Prior to the invention described in my aforementioned copending application, organic adhesive had been used to bond semiconductor devices to metal lead frames and other substrates. Typical die attach adhesives which had been used for this purpose include either epoxy or polyimide material and precious metal. The improved rapidly curing adhesive described in my copending application contains a cyanate ester, alkylphenol and metal curing catalyst. Adhesive formulations of the type described have the property of being able to be cured in a very short time at relatively low temperature, i.e., 5 minutes or less, at 200.degree. C. This cyanate ester adhesive formulation generally includes 60 to 90 wt. % of an electrically and/or thermally conductive filler. Typical electrically conductive fillers useful in the formulation are silver or nickel.
I have now determined it is not necessary to include as much silver in the adhesive formulation and that a small but effective amount of silver may be incorporated in a cyanate ester-containing adhesive formulation to reduce the curing time at a temperature less than the glass transition temperature of the cyanate ester-containing adhesive. More particularly, I have discovered that as little as up to 15% to 20% of silver, present as either uncoated flake and powder particles or flake and powder particles coated with surfactants (as normally purchased commercially), can be effective to significantly reduce the curing time of a cyanate ester-containing adhesive when present with a curing co-catalyst such as an alkylphenol and/or a metal compound of, for example, cobalt. I have also discovered that co-curing catalysts may be omitted and that somewhat greater amounts of silver alone will function as a catalyst to achieve rapid curing when no curing co-catalyst is present.